I posit that the second interpretation is the preferred, and Miss Kitty broke something valuable or perchance nearly killed a human. As a result, and also because of the general stress of the coming apocalypse, Willow and Tara gave her for adoption to a loving family in a faraway region with much less demon activity. Miss Kitty Fantastico lived to a respectable old age and died peacefully in her sleep surrounded by those who loved her and didn't think to have crossbows lying around the house. the end